I. Field of the Invention
The present invention relates to radio communications. More particularly, the present invention relates to power control in a radiotelephone system.
II. Description of the Related Art
The Federal Communications Commission (FCC) governs the use of the radio frequency (RF) spectrum. The FCC allocates certain bandwidths within the RF spectrum for specific uses. A user of an allocated bandwidth of the RF spectrum must take measures to ensure that the radiated emissions inside and outside of that bandwidth are maintained within acceptable levels to avoid interfering with other users operating in the same and or other bandwidths. These levels are governed by both the FCC and the particular user groups of said bandwidth.
The 800 MHz cellular telephone system operates its forward link, the cell to radiotelephone transmission, in the bandwidth of 869.01 MHz to 893.97 MHz and the reverse link, the radiotelephone to cell transmission, in the bandwidth of 824.01 MHz to 848.97 MHz. The forward and reverse link bandwidths are split up into channels each of which occupies a 30 kHz bandwidth. A particular user of the cellular system may operate on one or several of these channels at a time. All users of the system must ensure that they are compliant with the level of radiated emissions allowable inside and outside of the channel or channels that they have been assigned.
There are several different techniques of modulation that can be used in the cellular telephone system. Two examples of modulation techniques are frequency division multiple access (FDMA) and code division multiple access (CDMA).
The FDMA modulation technique generates signals that occupy one channel at a time while the CDMA modulation technique generates signals that occupy several channels. Both of these techniques must control their return link radiated emissions to within acceptable limits inside and outside of the assigned channel or channels. For maximum system performance, users of the CDMA technique must carefully control the level of radiated power inside the channels in which they are operating.
FIG. 1 shows a typical cellular radiotelephone. In both an FDMA and a CDMA based radiotelephone, there exists the possibility of driving the power amplifier (101) in the transmitter beyond a point where acceptable out of channel radiated emissions are maintained. This is primarily due to the increased distortion output levels of the power amplifier (101) at high output powers. Also, driving the power amplifier (101) beyond a certain point can cause interference internal to the radio. For example, PA puncturing in CDMA affects synthesizer phase noise due to large current transitions. Both of these issues cause unacceptable radio performance.
Maintaining the proper on-channel output power can be difficult due to several undesirable effects in the radiotelephone hardware. For example, the CDMA based radio must implement a power control system that operates over a very wide dynamic range, 80 dB to 90 dB, such that the transmitted output power is linearly related to the received input power.
Closed loop and open loop power control together determine the return link transmit energy, as disclosed in U.S. Pat. No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Incorporated. Therefore, the linear and nonlinear errors produced in both the receiver (103) and transmitter (102) RF sections can cause unacceptable power control performance. Also, both the FDMA and CDMA based radios must operate on different channels while maintaining acceptable output power levels. Variation in output power level and input power detection versus frequency can cause an unacceptable amount of error in the amount of return link transmitted energy.
These issues present significant problems to the designer of both FDMA and CDMA based radiotelephones. There is a resulting need for an effective, cost efficient means of correcting these problems.